1. Field
Aspects of embodiments of the present invention relate to a secondary battery.
2. Description of the Related Art
Lithium ion secondary batteries are widely used in electronic devices such as notebook computers and cellular phones. Such lithium ion secondary batteries are superior to other types of secondary batteries in terms of power, capacity, and weight, and are also used in hybrid vehicles and electric vehicles.
Lithium ion secondary batteries for vehicles should satisfy the requirements of safety and reliability under harsh conditions. A penetrating test, a squeezing test, and an overcharging test are the harshest of safety tests.
Of these safety tests, the penetrating test and the squeezing test are very important in predicting damage to a secondary battery due to a vehicle accident. Particularly, the penetrating test and the squeezing test require that even after a nail penetrates a secondary battery, or a secondary battery is squeezed, the temperature of the secondary battery does not excessively increase.